Why glass is more sustainable than plastic

Glass is a natural material that can be produced spontaneously even without human intervention when intense heat melts sand. An ancient form of glass called obsidian is formed during volcanic eruptions and its use as spear tips can be traced back 280,000 years. This is 80,000 years before our ancient ancestors evolved into homo sapiens!

Ancient form of glass was used for spear tips and arrowheads 280,000 years ago

Even though the production of glass has evolved significantly, it is still made from natural abundant materials such as sand, soda ash (sodium carbonate) and limestone. It is a very safe material to the environment as it does not leak any substance into the soil, water or air. This contrasts with plastic, which releases different types of chemicals into the soil and sea as discussed in this National Geographic article. Some of these chemicals also leak into food and water we store inside plastic containers as explained in this post.

Glass is produced by melting sand, soda ash and limestone at high temperatures.

However, there are several articles on the internet comparing the manufacturing carbon footprint of PET plastic bottles against that of glass ones and concluding PET plastic bottles are more sustainable. How can it be? And how to choose the best option?

Let’s first compare the manufacturing process of both, their raw material consumption and greenhouse gas (GHG) emission in equivalent measures. The table below compares the amount of abiotic material, water and greenhouse gas emission to manufacture each gram of glass and plastic, according to The Waste and Resource Action Programme,:

Material used

Glass (per g)

Plastic (per g)

Less material/emission per gram

Abiotic material

3.04 g

6.45 g

GLASS

Water

17.1 g

294.2 g

GLASS

GHG emission

0.716 g

3.723 g

GLASS

By analysing the information provided, we can conclude that the manufacture of glass is more sustainable or less raw-material intensive than plastic. However, we need to consider the final product to calculate the total usage of raw material and GHG emission of each overall process. In the manufacture of bottles, for example, the glass version can be up to 20 times heavier than a PET plastic bottle. In order for glass final products to be better in terms of GHG emissions, they need to be no more than 5 times heavier than their plastic versions.

Glass bottles can weight up to 20 times more than PET plastic ones

This is the argument the beverage industry uses to justify their choice for plastic bottles. They even add the additional transportation needed to carry the bulky, heavy glass bottles in the calculation to make plastic bottles look even more attractive. Despite this, you have to remember PET plastic bottles are toxic, made with fossil fuels (non-renewable resources) and are not naturally degradable. They can cause diseases and pollute oceans and soil.

PET plastic bottles are mostly used for water and soft drinks and can be avoided by favouring filtered tap water and other packaging options such as cans. Although PET plastic bottles may emit less GHG in total, it may not be true for other plastic containers which are heavier, such as reusable bottles, bowls and kitchen utensils in general. Innovation in the glass production industry has already reduced glass bottles weight by 50% in the last 20 years and further reduction is expected in the future.

The table below compares standard weight plastic and glass bottles and their light weighted versions with reusable plastic bottles. All bottles have 355 ml of capacity.

PET plastic containers

Reusable plastic bottle

Glass bottle

Container weight

18.9 gram

12.7 gram

50 gram

256 gram

170 gram

Abiotic material

122

82

322.5

778

517

Water

5560

3736

14710

4378

2907

GHG emission

70

47

186.15

183

122

As you can see, for reusable containers, glass is better than plastic, except for the total abiotic material. But as abiotic material in the case of glass is sand and other abundant non-toxic substances and not petroleum, we can conclude it is a safer material.

To conclude, we list some tips to be greener when choosing between plastic and glass:

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Published by Bruna Moreira

MBA candidate at London Business School, I am passionate about finding simple solutions to world-scale concerns, such as climate change effects. Here I will explain how green building and small adaptations in your home can help our planet. Welcome!
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Our mission is to raise awareness, educate and connect people for the construction of new sustainable homes and the improvement of existing ones. Here you are going to find many simple solutions to give your contribution to the environment with little and big step changes in your home and household habits every day!